Description will be made by using as an example a terminal plate circuit within terminal boxes for solar cell panel that are arranged in a large number on a roof of a house or the like. FIG. 1 shows a schematic view of a rear surface of a solar cell panel. As is clear from FIG. 1, each solar cell panel 10 has a terminal box 12 mounted on a rear surface thereof. Terminal boxes 12 of adjacent solar cell panels 10 are electrically connected with each other via an external connection cable 14.
In the inside of the terminal box, a pair of terminal plates are mounted, one end thereof is connected to the external connection cable, and the other end thereof is connected to the electrode of the solar cell panel. Further, a diode is incorporated in the inside of the terminal box so as to connect the aforesaid pair of terminal plates with each other.
This diode is a bypass diode for short-circuiting the electric current, which is generated by application of an inverse-direction voltage when the electromotive force of the solar cell panel decreases, from one external connection cable to the other external connection cable. When the diode performs the aforementioned function, a large electric current flows in the forward direction of the diode, so that the diode generates heat violently, and the temperature thereof may exceed a proper operating temperature of the diode. In such cases, not only will the diode fail to function as a diode (heat burst) but also the diode and the surrounding circuit may have a fear of being broken. Further, even if they are not broken, the life of the diode will be extremely shortened when such a heat burst is repeated. Therefore, the generated heat must be efficiently dissipated so that the heat generated during the operation of the diode may not exceed a proper operating temperature of the diode.
As means for efficiently dissipating the heat generated by a diode, proposed is a terminal plate circuit in which a terminal plate is enlarged as much as possible within a terminal box, and the bottom surface of the diode is soldered onto the surface of the terminal plate so that the heat of the diode may be easily dissipated towards the terminal plate (cf. Japanese Patent Application Laid-Open (JP-A) Nos. 2005-251962 and 2007-110031).
However, when the bottom surface of the diode is soldered and attached to the surface of the enlarged terminal plate, air bubbles are mixed into the solder during the soldering, and the air bubbles lower the efficiency of heat transfer from the diode to the terminal plate, whereby the heat of the diode is not efficiently dissipated.